Aim: The aim of the research is to determine characteristic of the correlation between climate and stroke through the analysis of relevant documents. Methods: We found 115 researches of temperature and season on stroke mortality/incidence and these were categorized according to location, meteorology, date span, data source and research sites’ latitudes. We divided the globe into 5 temperature zones based on latitude ranges: 0 - 10, 10 - 23.5, 23.5 - 40, 40 - 50, and >50 degrees, and allotted a zone to each country. Stroke mortality by five temperature zones was calculated per 100,000 people. Results: 70% of the researches came from latitudes greater than 40 degrees with 92% of researches located in Europe, USA, and Asia. The mortality range was 42 - 63 per 105 individuals within latitudes 0 - 40 degrees. In latitudes 40 - 66.5 degrees, a linear upward trend (y = 69.82x − 22.823, R2 = 0.99) was noticed. More than 75% of the research reports indicated a negative correlation between climate and stroke, and the proportion was almost 6 and 7 times greater than that of the fluctuation and non-correlation, respectively. The most frequently used research methods were regression analysis and time series analysis. Conclusion: All of the research results confirmed that lower temperature is associated with higher mortality and incidence of stroke, while higher latitude is correlated with higher stroke mortality, consistent with the temperature zones.
Stroke represents the third leading cause of death worldwide [
Past researches have generated a large amount of data on the relationship between climate and stroke, and the results and perspectives show great diversity. The aim of our research is to analyze the differences and characteristic of these reports, and to provide theoretical basis for the study of the relationship between climate and stroke.
We only obtained data on stroke deaths and population denominators in 192 countries in 2002 from WHO websites [
We found 115 researches of climate on stroke mortality/incidence and these were categorized according to location, meteorology, method, date span, data source and research sites’ latitudes. Average temperature was reported by month, season, or year, although some researches just reported season without reference to temperature. A negative relationship was defined as the lower the temperature, the higher stroke mortality/incidence; alternatively the coldest season has the highest mortality/incidence. Fluctuation was defined as a higher mortality/incidence of stroke with the temperature fluctuations with noncorrelation defined as invariant mortality/incidence stroke in respect of variation of temperature however defined temporally.
Stroke mortalities according to the five temperature zones were calculated by per 100,000 people and represented by the line chart. The corresponding proportions of research reports on the correlation between climate and stroke by location were calculated and listed in the table. The proportions of methods for data analysis in various researches were determined and illustrated by the pie chart.
Data entry and statistical analysis were completed using Microsoft Office Excel and SPSS 16.0, respectively.
Total | Location | Northern Hemisphere | Southern Hemisphere | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
World | Europe | North America | South America | Asia | Oceania | Africa | 23.5˚ - 40˚ | 40˚ - 50˚ | >50˚ | <23.5˚ | 23.5˚ - 40˚ | |||
Meteorology | ||||||||||||||
Temperature | 70 | 1 | 23 | 13 | 3 | 27 | 1 | 2 | 19 | 30 | 12 | 1 | 6 | |
Season | 45 | 1 | 17 | 13 | 1 | 8 | 3 | 2 | 4 | 27 | 8 | 0 | 5 | |
Data Source | ||||||||||||||
Mortality register | 29 | 0 | 15 | 5 | 1 | 7 | 1 | 0 | 5 | 11 | 12 | 0 | 3 | |
Incidence register | 50 | 1 | 17 | 13 | 2 | 15 | 1 | 1 | 8 | 31 | 5 | 0 | 4 | |
Hospital admission | 36 | 1 | 8 | 8 | 1 | 13 | 2 | 3 | 11 | 15 | 3 | 1 | 4 | |
Years Span | ||||||||||||||
<1 | 16 | 1 | 7 | 2 | 0 | 4 | 0 | 2 | 3 | 9 | 1 | 0 | 2 | |
1 - 5 | 46 | 1 | 15 | 7 | 4 | 18 | 0 | 1 | 14 | 21 | 5 | 0 | 5 | |
5 - 10 | 33 | 0 | 12 | 9 | 0 | 7 | 4 | 1 | 2 | 17 | 9 | 1 | 4 | |
>10 | 17 | 0 | 5 | 7 | 0 | 5 | 0 | 0 | 4 | 8 | 5 | 0 | 0 | |
No | 3 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 2 | 0 | 0 | 0 |
Category | Number of researches | Negative correlation Proportion (%) | Positive correlation Proportion (%) | Fluctuation correlation Proportion (%) | Noncorrelation Proportion (%) | ||
---|---|---|---|---|---|---|---|
Total | Temperature | 69 | 76.81 | 1.45 | 14.49 | 7.25 | |
Season | 46 | 78.26 | 2.18 | 6.52 | 13.04 | ||
Location | |||||||
World | Temperature | 1 | 100.00 | 0.00 | 0.00 | 0.00 | |
Season | 1 | 100.00 | 0.00 | 0.00 | 0.00 | ||
Europe | Temperature | 23 | 86.96 | 13.04 | 0.00 | 0.00 | |
Season | 17 | 70.59 | 0.00 | 11.76 | 17.65 | ||
North America | Temperature | 14 | 64.28 | 0.00 | 14.29 | 21.43 | |
Season | 13 | 84.62 | 0.00 | 0.00 | 15.38 | ||
South America | Temperature | 2 | 50.00 | 0.00 | 50.00 | 0.00 | |
Season | 1 | 100.00 | 0.00 | 0.00 | 0.00 | ||
Asia | Temperature | 26 | 76.92 | 3.85 | 11.54 | 7.69 | |
Season | 8 | 75.00 | 0.00 | 12.50 | 12.50 | ||
Oceania | Temperature | 1 | 0.00 | 0.00 | 100.00 | 0.00 | |
Season | 4 | 100 | 0.00 | 0.00 | 0.00 |
analysis were found to be the most frequently used research methods, accounting for 33.91% and 20%, respectively. The proportion of the sinusoidal/cosinor method was lowest (4.35%).
All findings point to the fact that lower temperature is the key climatic variable for stroke. Approximately 80% of the research reports were in support of a negative correlation between the average temperature and stroke, demonstrating an increase in mortality as the temperature decreases. Stroke mortality peaks in winter, the season with the lowest temperature. Therefore, the research results of both average temperature and seasonal factors reveal that lower temperature increases the mortality and incidence of stroke.
Temperate or boreal regions include over 90% of the researches located in Europe, America, and Asia, showing that temperature of the cold regions was the main research focus. Based on the 5 temperature zones, we further calculated stroke mortality and found negative effects of temperature for stroke that at latitudes > 40 degrees, the higher latitude the higher stroke mortality. In other words, the lower temperature, the higher mortality of stroke in temperate or boreal regions. Lower temperatures in temperate and boreal regions were associated with stroke mortality that was twice as high compared to tropical and subtropical regions (126/105 vs. 58/105). Temperatures in the tropical and subtropical regions did not affect stroke mortality as mortality was stable.
It is worth noting that in the southern hemisphere stroke mortality demonstrated a smooth linear upward trend from the tropic to boreal regions. However, mortality rates in the tropic and subtropical regions of the southern hemisphere are close to those in the northern hemisphere with values of 42 - 63/105 in both hemispheres. In only 2 countries residing in the temperate and boreal region was an upward trend observed. Thus, the impact of temperature on stroke in both hemispheres is consistent.
11 of the 115 also researches demonstrated noncorrelation between temperature and stroke. Temperatures were mild in 6 of these 11 researches (regions with warm winters), with 3 researches located geographically in maritime climate [
A variety of methods have been utilized to investigate the relationship between climate and stroke. Regression analysis and time series analysis were the most widely used methods, and were applied in more than half of the researches. These methods are valuable for evaluating the relationship between climate and stroke.
Global data in our analysis were derived from stroke deaths and population worldwide (rather than regional and sampling), consider the calculated results to be reliable, although researches in one region (Hong Kong) showed conflicting results [
In summary, this document analysis confirmed that lower temperature increases the mortality and incidence of stroke, and higher latitude is associated with higher stroke mortality, in accordance with the temperature zones.
The research was supported by the Natural Science Foundation of Inner Mongolia in China (No. 2013MS1124) and the Inner Mongolia Medical University Students Innovation and Entrepreneurship Program Training Project Autonomous Region (No. 201810132010).
We have no competing interests.
Li, H.W., Qian, Y.G.., Wang, S.B., Zhang, H.R., Gou, W.F., Niu, M.Z., Yu, D., Wu, R.J., Gao, L.Q., Chi, B.F., Wang, Q.X., Hao, W.L., Li, W., Yan, T., Niu, L.W., Liu, Y., Zhao, J., Jin, Y., Du, M.L. and Sun, J. (2019) Document Analysis of Correlation between Climate and Stroke. Open Journal of Epidemiology, 9, 82-88. https://doi.org/10.4236/ojepi.2019.91008